JP2000160014A - Silicone rubber composition and electrical wire coated with silicone rubber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a void-free, good cured material by incorporating into a rubber composition an organopolysiloxane, a finely divided silica filler and an organic peroxide having a primary particle diameter and a maximum particle diameter respectively not greater than a specific value, in a specified amount of each of the components. SOLUTION: A rubber composition comprises 100 pts.wt. organopolysiloxane which is preferably terminated at each molecular end with a triorganosilyl group or hydroxyl group and is represented by the formula: R'SiO(4-a)/2 (wherein R' is a monovalent hydrocarbon; and (a) is a number of 1.90-2.05), 5-100 pts.wt. finely divided silica filler and 0.5-5 pts.wt. organic peroxide which has a primary particle diameter of not greater than 12 μm and a maximum particle diameter of not greater than 20 μm and is represented by the formula (wherein (n) is an integer of 0-3). The rubber composition is vulcanized by hot air under normal pressure at a temperature of 200-500 deg.C for 5 sec-10 min to produce an elastic material. The organic peroxide includes bisbenzoyl peroxide, bis(o-methylbenzoyl) peroxide, bis(p-methylbenzoyl)peroxide or the like.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a silicone rubber composition and a silicone rubber-coated electric wire having a cured product thereof as a coating layer.

[0002]

2. Description of the Related Art Silicone rubber is widely used in various fields because of its excellent heat resistance, cold resistance, electrical insulation and the like, and various processing processes are carried out depending on the application.

[0003] Silicone rubber is vulcanized by various methods depending on the type of rubber and the physical properties required for the cured product, and particularly, by heat treatment in the presence of an organic peroxide. Vulcanization methods are widely used. And, as the organic peroxide as a vulcanizing agent, benzoyl peroxide, p-chlorobenzoyl peroxide, 2,4-dichlorobenzoyl peroxide, dicumyl peroxide,
Examples thereof include di-t-butyl peroxide, 2,5-dimethyl-2,5-di (t-butylperoxy) hexane, t-butylperbenzoate, and t-butylcumyl peroxide. In particular, as a vulcanizing agent for obtaining a molded product such as a coating layer or a sheet of an electric wire by extrusion hot air vulcanization, 2,4-
Dichlorobenzoyl peroxide is the only used.

[0004]

However, 2,4-dichlorobenzoyl peroxide is not only corrosive to metals, but the cured silicone rubber obtained by using it has a high heat resistance under sealing. The properties and compression set were not always satisfactory.

[0005] Therefore, t-butylperoxyoctadecyl carbonate, t-amylperoxy-2,6,8-
T-Alkyl peroxyalkyl carbonates have been proposed, such as trimethyl-4-nonyl carbonate, t-amyl peroxyoctadecyl carbonate (see U.S. Pat. No. 4,061,704). However, this organic peroxide leaves a residue having a large molecular weight, so that not only is it difficult to remove the residue, but also the residue has a problem that the heat resistance of the silicone rubber deteriorates.

[0006] On the other hand, with respect to normal pressure hot air vulcanization of silicone rubber, a method is known in which an unsaturated group-containing silicone rubber is subjected to an addition reaction with an organohydrogenpolysiloxane in the presence of a platinum-based catalyst. However, this method has a problem that the pot life is short and the scorch is easily generated as compared with the method using an organic peroxide.

[0007] Furthermore, due to the recent trend of increasing interest in the environment, the amount of 2,4-dichlorobenzoyl peroxide that generates halogen-based harmful substances as a vulcanizing agent tends to decrease year by year. Yes, there is a shift to the use of non-chlorine peroxides. In particular, for organic peroxides for normal pressure hot air vulcanization that requires versatility, bis (o-methyl)
Benzoyl peroxide (see JP-A-59-18758 and JP-A-62-263254), bis (dimethyl-substituted benzoyl) peroxide (see JP-A-60-16968), bis (trimethyl-substituted benzoyl) ) Peroxide (see JP-A-60-163860), bis (o-methoxybenzoyl) peroxide (see JP-A-59-232145), bis (p-methylbenzoyl) peroxide (Japanese Patent Publication No. No. 50327)). According to these substances, prevention of blooming due to decomposition residues at the time of hot-air vulcanization under normal pressure, improvement of surface tackiness, and resolution of safety and health problems are achieved.

However, when the acyl peroxide is subjected to hot-air vulcanization under normal pressure, there is a problem that voids are generated in the obtained silicone rubber molded product. Has a problem that spark-out occurs.

The present invention has been made to solve these problems, and provides a silicone rubber composition capable of forming a cured product having good properties without voids by hot air vulcanization or the like. The purpose is to: It is another object of the present invention to provide a silicone rubber-coated electric wire having a cured product having good properties without voids as a coating layer.

[0010]

Means for Solving the Problems As a result of intensive studies to achieve the above object, the present inventors have found that a silicone rubber composition comprising an organopolysiloxane and a finely divided silica-based filler has been finely divided. By adding the acyl-based organic peroxide, it has been found that a silicone rubber composition which can be subjected to continuous normal-pressure hot air vulcanization and free from voids can be obtained, and the present invention has been completed.

[0011] That is, the silicone rubber composition of the present invention, (A) the general formula ^{_{R 1 a SiO (4-a}} ) / 2 ( in the formula, R ¹
Is an unsubstituted or substituted monovalent hydrocarbon group, a is 1.90 to 2.05
Indicates a positive number. Organopolysiloxane represented by)
100 parts by weight and (B) a finely divided silica-based filler 5 to 100
Parts by weight and (C) general formula

Embedded image (Wherein, n represents an integer of 0 to 3), and contains 0.5 to 5 parts by weight of an organic peroxide having a primary particle size of 12 μm or less and a maximum particle size of 20 μm or less. It is characterized by the following.

The present invention will be described in detail below.

The organopolysiloxane of the component (A) constituting the silicone rubber composition of the present invention has the general formula R ¹
_a Represented by SiO 2 _{(4-a) / 2} . Here, R ¹ is an alkyl group such as a methyl group, an ethyl group, a propyl group, a butyl group, a vinyl group, an allyl group, a butaniel group, a phenyl group,
In a aryl group such as a tolyl group, or a hydrocarbon group thereof, a chloromethyl group, a chloropropyl group, or a chloropropyl group in which part or all of hydrogen atoms bonded to carbon atoms are substituted with a halogen atom, a cyano group, or the like -One or more unsubstituted or substituted monovalent hydrocarbon groups selected from a trifluoropropyl group, a 2-cyanoethyl group and the like.
A is a positive number between 1.90 and 2.05.

The organopolysiloxane preferably has a straight-chain molecular skeleton, but may contain a branched portion in the molecule. In addition, the molecular terminal
It is preferable to block with a triorganosilyl group or a hydroxyl group. Examples of the triorganosilyl group include a trimethylsilyl group, a dimethylvinylsilyl group, a methylphenylvinylsilyl group, a methyldiphenylsilyl group, a methyldivinylsilyl group, and a trivinylsilyl group. The degree of polymerization is not particularly limited, but, from the viewpoint of strength after curing, the degree of polymerization is such that it exhibits a raw rubber state at room temperature, that is, 25.
It is preferable to use one having a degree of polymerization such that the viscosity at ℃ is 3,000 cSt or more.

The finely divided silica-based filler of the component (B) in the present invention is compounded for the purpose of reinforcing, thickening, improving processability, increasing the amount of fumed silica, and the like.
Examples include wet silica, fumed silica or silica having a surface subjected to a hydrophobic treatment, fine silica powder, diatomaceous earth, and the like. As such a finely divided silica-based filler, a filler having a specific surface area of 1 m ² / g or more is preferably used.

Further, the compounding amount of the finely divided silica-based filler is determined according to the above-mentioned organopolysiloxane of the component (A).
5 to 100 parts by weight for 100 parts by weight. If the amount of the finely divided silica filler is less than 5 parts by weight, the desired reinforcing effect cannot be sufficiently obtained, and the workability is also insufficient.
If the amount of the fine silica filler exceeds 100 parts by weight, not only the processability such as extrudability becomes extremely poor, but also the properties such as heat resistance deteriorate, so that especially the electric wire Is not suitable for use as a coating material. A more preferred range is 20 to 80 parts by weight based on 100 parts by weight of the organopolysiloxane (A).

The organic peroxide represented by the above general formula (I) as the component (C) used in the present invention includes bisbenzoyl peroxide, bis (o-methylbenzoyl) peroxide and bis (m-methylbenzoyl). ) Peroxide, bis (p-methylbenzoyl) peroxide, bis (dimethyl-substituted benzoyl) peroxide, bis (trimethyl-substituted benzoyl) peroxide and the like. Particularly, use of bis (p-methylbenzoyl) peroxide, that is, bis (4-methylbenzoyl) peroxide is preferred from the viewpoint of stability. These organic peroxides act as a vulcanizing agent for the organopolysiloxane of the above-mentioned component (A). However, since they do not contain a halogen atom in the molecule, they are decomposed to cause halogens which are harmful to health and safety. Does not produce substances.

The amount of the organic peroxide (C) is 0.1 to 5 parts by weight based on 100 parts by weight of the organopolysiloxane (A). (C) The amount of component
If the amount is less than 0.1 part by weight, vulcanization becomes insufficient and desired characteristics cannot be obtained, so that it cannot be put to practical use. Conversely, (C)
If the amount of the component exceeds 5 parts by weight, it is not preferable because not only unnecessary cost is increased but also an adverse effect is caused by excessive decomposition residue.

Further, in the organic peroxide of the component (C), the primary particle diameter is reduced to 12 μm or less, more preferably 5 to 8 μm, and the maximum particle diameter is reduced by making the particles finer. Reduce to 20μm or less. In addition, in order to add an organic peroxide, it is usually used to add and disperse an organic peroxide to a high-viscosity organopolysiloxane in advance, but this dispersion state is extremely important in the properties of a cured product. In this case, it is preferable to use an organic peroxide having no aggregate formed by partially aggregating the organic peroxide.

When an organic peroxide aggregated or an organic peroxide having a particle diameter of more than 20 μm is used, honeycomb-like or large-diameter voids are easily generated during vulcanization. In a silicone rubber-coated electric wire having a sulfur cured product as a coating layer, spark-out easily occurs. Therefore, in the present invention, it is desirable to use, as the vulcanizing agent of the component (C), an organic peroxide in which the primary particle diameter and the maximum particle diameter are respectively adjusted to the above ranges and the generation of aggregates is eliminated.

The silicone rubber composition of the present invention can be obtained by uniformly mixing predetermined amounts of the above components (A) to (C). Although there is no particular limitation on the order of blending these components, usually, after the organopolysiloxane of the component (A) is mixed with the silica-based filler of the component (B), it is further mixed with the organic peroxide of the component (C). What is necessary is just to add a substance and mix by kneading with a roll. The composition thus obtained includes a dispersant such as a low molecular weight siloxane having a degree of polymerization of 100 or less, a silane containing a silanol group, a silane containing an alkoxy group, and a heat resistance improver such as iron oxide, cerium oxide, and iron octylate. , A pigment, and other additives which are added to a usual silicone rubber composition can be optionally added.

The thus obtained silicone rubber composition of the present invention is cured by heating and vulcanization to form an elastic body. The vulcanization is performed by normal pressure hot air vulcanization, for example, by heating at a temperature of 200 to 500 ° C. for 5 seconds to 10 minutes, or by additionally using heating with an infrared heater, without any voids or surface tack, An elastic body having excellent heat resistance can be obtained. Thus, the composition of the present invention
It is particularly useful as a cable coating material and a molding material for tubes, sheets, and the like.

Furthermore, a silicone rubber sponge having highly uniform cells can be obtained by further blending a known foaming agent and a known curing agent with the composition of the present invention. As the blowing agent, azo compounds such as azobisisobutyronitrile, 1,1'-azobis-1-acetoxy-1-phenylethane, azodicarboxylic acid amide,
Dinitrilopentamethylenetetramine, N, N-dimethyl-
Examples include nitroso compounds such as N, N-dinitrosoterephthalic acid amide.

The silicone rubber composition of the present invention thus constituted can be subjected to continuous normal-pressure hot air vulcanization, and by this vulcanization, it is possible to obtain a cured silicone rubber product having no voids and excellent properties. Can be. Further, in a silicone rubber-coated electric wire having a coating layer made of such a cured silicone rubber, no spark-out occurs in a spark test and no decrease in heat resistance is observed. Further, since the organic peroxide used as a vulcanizing agent does not contain a halogen element, it does not generate halogen-based harmful substances by decomposition, and there is no problem in terms of environmental health and safety.

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described with reference to examples, but the scope of the present invention is not limited by these examples. In the following description, “part” indicates “part by weight”, and “viscosity” indicates a value measured at 25 ° C.

Examples 1 to 3 (Comparative Examples 1 and 2) 99.75 mol% of (CH ₃ ) ₂ SiO units and (CH ₂ ＣC
H) 100 parts of an organopolysiloxane (viscosity 10,000,000 cst), which is composed of 0.25 mol% of CH ₃ SiO units and both ends are capped with a dimethylvinylsilyl group, and fumed silica Aerosil 200 (a product of Nippon Aerosil Co., Ltd.) Name) 40 parts and 4 parts of diphenylsilanediol as a dispersing agent were added and kneaded uniformly,
After a heat treatment for 4 hours, the mixture was plasticized with two rolls to prepare a base compound.

Next, in this base compound, Table 1
A bis (p-methylbenzoyl) peroxide or a bis (o-methylbenzoyl) peroxide having a primary particle diameter and a maximum particle diameter shown in (1) is mixed and dispersed in the above-mentioned organopolysiloxane at a concentration of 50% by weight. 1.5 parts of sulfuric acid paste was added and kneaded with two rolls.

Next, the silicone rubber compositions obtained in Examples 1 to 3 and Comparative Examples 1 and 2 were applied to a tin-plated annealed copper wire having an outer diameter of 3 mm using an extruder having a diameter of 40 mm. After extrusion coating, the resultant was subjected to normal pressure hot air vulcanization in a hot air furnace maintained at a temperature of 400 ° C. so that the residence time was 15 seconds. No post-vulcanization was performed.

Next, a spark test was performed on the silicone rubber-coated electric wire thus obtained. In the spark test, the number of occurrences of spark-out when a 10,000 m wire was drawn at a voltage of 5 Kv and a wire speed of 80 m / min was measured. The number of occurrences of 0 was OK, and the occurrence of 1 or more was NG. After measuring the initial properties (tensile strength and elongation) of the silicone rubber coating layer, the same properties were measured after a lapse of 96 hours at 220 ° C. to determine the rate of change. These test results and measurement results are shown in the lower column of Table 1, respectively.

[Table 1] Further, using a vulcanizing agent paste having an aggregate in which bis (p-methylbenzoyl) peroxide was partially aggregated, a silicone rubber composition was prepared in the same manner as in Example 1, and the silicone rubber composition was heated and heated under normal pressure. Vulcanized. An electron micrograph of the obtained cured product is shown in FIG.

From this photograph, it was confirmed that, in the cured product vulcanized with an organic peroxide (acyl peroxide) having an aggregate, honeycomb-like voids were generated in the aggregate portion. In addition, Table 1 shows that the use of acyl peroxide having an aggregate as a vulcanizing agent for the coating layer of the silicone rubber-coated electric wire increases the incidence of spark-out. Then, it was confirmed that by using a peroxide having a controlled particle diameter among the above-mentioned peroxides as a vulcanizing agent, a decrease in characteristics due to heat treatment can be reduced, and occurrence of spark-out in a spark test can be reduced.

[0031]

As is apparent from the above description, according to the silicone rubber composition of the present invention, a cured product having good properties without voids can be formed by hot air vulcanization or the like. Further, in a silicone rubber-coated electric wire in which a coating layer is constituted by a cured product of such a silicone rubber composition, no spark-out occurs in a spark test, the heat resistance is high, and the characteristic deterioration due to heating is small.

[Brief description of the drawings]

FIG. 1 is an electron micrograph showing the structure of a cured product obtained from a silicone rubber composition containing an acyl peroxide paste having aggregates.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01B 3/46 H01B 3/46 H (72) Inventor Sumikaga Kiyogami 6-2-31 Roppongi, Minato-ku, Tokyo No. Toshiba Silicone Corporation (72) Inventor Minoru Osato 6-2-1, Roppongi, Minato-ku, Tokyo F-term in Toshiba Silicone Corporation 4J002 CP031 CP061 CP141 DJ016 EK047 FD016 GQ01 4J038 DL031 HA446 JA66 JC32 KA08 KA20 PB09 5G305 AA02 AA14 AB24 AB40 BA15 BA22 CA26 CB05 CB14 CC02 CD01 CD05

Claims (3)

[Claims] (A) The general formula R ¹ _a SiO
100 parts by weight of an organopolysiloxane represented by _{(4-a) / 2} (wherein R ¹ is an unsubstituted or substituted monovalent hydrocarbon group, and a is a positive number from 1.90 to 2.05); ) 5-100 parts by weight of a finely divided silica-based filler and (C) a general formula (Wherein, n represents an integer of 0 to 3), and contains 0.5 to 5 parts by weight of an organic peroxide having a primary particle size of 12 μm or less and a maximum particle size of 20 μm or less. A silicone rubber composition comprising: 2. The organic peroxide as the component (C),
The silicone rubber composition according to claim 1, which is bis (4-methylbenzoyl) peroxide. 3. A silicone rubber-coated electric wire comprising, as a coating layer, a cured product obtained by subjecting the silicone rubber composition according to claim 1 or 2 to hot air vulcanization.